Genereally you will find that is a UTI goes untreated (as it often can as it may not present obvious sypmtoms) it will progress to a kidney infection.

You can tell it is a kidney infection as you will have cramp like stabbing pains in you back, between the bottom of your ribs and the top of your hips on one or both sides. You can help relieve the pain by massaging downwards with your hand quite hard - this will help manually remove the build up in your kidney and help it to clean itself.

Drink plenty of water, the ABs will clear it up - the ABs should be fine with your DS so long as the dr knew you were BF when he prescribed them?

anyway, it will pass - I had a severe double kidney infection and it was painful as hell! So !!